Steam reforming is a method for producing hydrogen and carbon monoxide by the reaction between a hydrocarbon and water vapor. The general chemical reaction of steam reforming is as follows:CmHn+mH2O→mCO+(m+n/2)H2 
The mixed gas (called “synthesis gas”) of hydrogen and carbon monoxide obtained by steam reforming is an important raw material in industries, which is a fundamental material in the field called C1 chemistry. It is used as the material for synthesizing methanol and dimethyl ether, and is also used as the material for Fischer-Tropsch reaction utilized for the production of gasoline and the like.
Conventionally, steam reforming of hydrocarbons is carried out using a nickel catalyst carried on alumina under conditions of high temperature and high pressure at about 700 to 830° C. and 15 to 40 atm.
However, the conventional steam reforming method has problems in that the selectivity to carbon monoxide (i.e., the ratio of the number of carbon atoms in the generated carbon monoxide based on the number of carbon atoms constituting the hydrocarbon) is relatively low, and various side reactions occur so that the products of the side reactions may clog the reaction tube and may deteriorate the catalyst. Further, since the reaction is carried out at a high temperature and high pressure, it is necessary to use a tough reaction apparatus which withstands to the high temperature and high pressure. Further, cost is required for the energy to realize the high temperature and high pressure.